Temperature compensated square function generator

Abstract

Temperature compensation may be provided to a square function generator by adjusting a tail current of the square function generator. Temperature compensation of the square function generator may be provided, for example, by a second square function generator circuit and an error amplifier. The second square function generator may be substantially similar to the first square function generator. The error amplifier is arranged in cooperation with the first and second square function generators such that the output of the error amplifier adjusts the tail current of the square function generators. A plurality of temperature square function generators may be configured to provide a temperature-compensated cubic function. The temperature compensated cubic function may be used for S-correction in a display system such as a cathode ray tube.

1. A temperature compensated function generator circuit, comprising:
 a first square function generator circuit, wherein the first square generator circuit includes a first non-inverting input, a first inverting input, a first control input, and a first output, wherein the first square function generator is capable of receiving an input signal via the first non-inverting input; 
 a second square function generator circuit, wherein the second square generator circuit includes a second non-inverting input, a second inverting input, a second control input, and a second output; 
 a third square function generator circuit, wherein the third square generator circuit includes a third non-inverting input, a third inverting input, a third control input, and a third output, wherein the first, second, and third inverting inputs are coupled together, wherein the second non-inverting input is coupled to the first inverting input, and wherein the third non-inverting input is coupled to the third inverting input; and 
 an error amplifier circuit, wherein the error amplifier circuit includes: an inverting error amplifier input that is coupled to the third output, a non-inverting error amplifier input that is coupled to the second output, and an error amplifier output that is coupled to the first, second, and third control inputs. 
 
   
   
     2. The temperature compensated function generator circuit as in  claim 1 , wherein each of the square function generator circuits is configured to provide a signal at the output of the square function generator circuit having a voltage that corresponds to approximately (VP−VN) 2 , wherein VP and VN correspond to voltages that are applied to a respective one of the non-inverting input and the inverting input of the square function generator circuit; and wherein the error amplifier circuit is arranged in cooperation with the second and third square function generator circuits to adjust a tail current in each of the square function generator circuits such that an error associated with each of the square function generator circuits is compensated via feedback. 
   
   
     3. The temperature compensated function generator circuit as in  claim 1 , further comprising:
 a first DC level shift circuit that is coupled between the first inverting input and the second non-inverting input; and 
 a second DC level shift circuit that is coupled between the third output and the non-inverting error amplifier input, wherein at least one characteristic of the first and second DC level shift circuits are approximately matched to one another. 
 
   
   
     4. The temperature compensated function generator circuit as in  claim 1 , further comprising: a voltage reference generator circuit having a reference output that is coupled to the first inverting input. 
   
   
     5. The temperature compensated function generator circuit as in  claim 1 , further comprising: a ramp generator circuit having a ramp output that is coupled to the first non-inverting input. 
   
   
     6. The temperature compensated function generator circuit as in  claim 1 , further comprising:
 an inverting amplifier circuit having an inverting amplifier input that is coupled to the first non-inverting input; 
 a fourth square function generator circuit, wherein the fourth square generator circuit includes a fourth non-inverting input, a fourth inverting input, a fourth control input, and a fourth output, wherein the fourth inverting input is coupled to an output of the first inverting amplifier circuit, the fourth non-inverting input is coupled to the first output, and wherein the fourth control input is coupled to the error amplifier output; 
 a fifth square function generator circuit, wherein the fifth square generator circuit includes a fifth non-inverting input, a fifth inverting input, a fifth control input, and a fifth output, wherein the fifth inverting input is coupled to an output of the first inverting amplifier circuit, the fifth non-inverting input is coupled to the first output, and wherein the fifth control input is coupled to the error amplifier output; and 
 a difference circuit, wherein the first difference circuit includes a first difference input that is coupled to the fourth output, a second difference input that is coupled to the fifth output, and a difference output, whereby the difference output is associated with a cubic function. 
 
   
   
     7. The temperature compensated function generator circuit as in  claim 6 , wherein the difference circuit comprises:
 a first op-amp circuit, wherein the first op-amp circuit includes an inverting op-amp input, a non-inverting op-amp input, and an op-amp output; 
 a first resistor that is coupled between the op-amp output and the inverting op-amp input; 
 a second resistor that is coupled between the fifth output and the inverting op-amp input; 
 a third resistor that is coupled between the fourth output and the non-inverting op-amp input; and 
 a fourth resistor that is coupled to the non-inverting op-amp input. 
 
   
   
     8. The temperature compensated function generator circuit as in  claim 6 , further comprising:
 a second inverting amplifier circuit having a second inverting amplifier input that is coupled the first output, and a second inverting amplifier output; 
 a sixth square function generator circuit having a sixth non-inverting input that is coupled to the first non-inverting input, a sixth inverting input that is coupled to the difference output, and a sixth control input that is coupled to the error amplifier output; 
 a seventh square function generator circuit having a seventh non-inverting input that is coupled to the first non-inverting input, a seventh inverting input that is coupled to the second inverting amplifier output, and a seventh control input that is coupled to the error amplifier output; and 
 a second difference circuit, wherein the second difference circuit includes a third difference input that is coupled to the sixth output, a fourth difference input that is coupled to the seventh output, and a second difference output, whereby the second difference output is associated with a quintic function. 
 
   
   
     9. A temperature compensated function generator circuit as in  claim 1 , wherein each of the square function generator circuits comprises:
 a first transistor, wherein a gate associated with the first transistor corresponds to a first input; 
 a second transistor having a source that is coupled to a source of the first transistor, wherein a gate associated with the second transistor corresponds to a second input; 
 a third transistor having a drain that is coupled to the source of the first transistor, 
 a fourth transistor having a gate that is coupled to a gate of the third transistor, a source that is coupled to a source of the third transistor, and a drain that is coupled to a drain of the first transistor and a drain of the second transistor, wherein the drain of the fourth transistor is associated with an output; 
 a first current-limiting device that is coupled between the drain of the first transistor and a first node, and 
 a second current-limiting device that is coupled between the drain of the second transistor and the first node. 
 
   
   
     10. The temperature compensated function generator circuit as in  claim 9 , wherein each of the square function generators further comprises:
 a first buffer circuit, wherein the drain of the first transistor is coupled to the drain of the fourth transistor through the first buffer circuit; and 
 a second buffer circuit, wherein the drain of the second transistor is coupled to the drain of the fourth transistor through the second buffer circuit. 
 
   
   
     11. The temperature compensated function generator circuit as in  claim 10 , wherein the first and second buffer circuits are source followers. 
   
   
     12. The temperature compensated function generator circuit as in  claim 9 :
 wherein the first current-limiting circuit comprises a fifth transistor having a source that is coupled to the drain of the first transistor, a gate that is coupled to the first node, and a drain that is coupled to the first node; and 
 the second current-limiting circuit comprises a sixth transistor having a source that is coupled to the drain of the second transistor, a gate that is coupled to the first node, and a drain that is coupled to the first node. 
 
   
   
     13. A temperature compensated function generator circuit, comprising:
 a first square function generator circuit; and 
 a means for compensation that is configured to provide temperature compensation for the first square function generator circuit by adjusting a tail current that is associated with the first square function generator circuit. 
 
   
   
     14. The temperature compensated function generator circuit as in  claim 13 , wherein the first square function generator circuit is configured to receive a first reference signal, and wherein the means for compensation comprises:
 a second square function generator circuit having an inverting input that is configured to receive the first reference signal, and further having a non-inverting input that is configured to receive a second reference signal, wherein the second reference signal is related to the first reference signal, and the second square function generator circuit is substantially similar to the first square function generator circuit; and 
 an error amplifier circuit having a non-inverting input that is coupled to the output of the second square function generator circuit, an inverting input that is configured to receive a third reference signal, and an output that is coupled to the first and square function generator circuits such that the error amplifier circuit is arranged to adjust a tail current of the first and second square function generator circuits, wherein the third reference signal is related to an offset error the second square function generator circuit, and wherein the error amplifier circuit is arranged in cooperation with the second square function generator circuit to adjust a tail current of the first and second square function generator circuit such that each of the square function generator circuits is compensated via feedback. 
 
   
   
     15. The temperature compensated function generator circuit as in  claim 14 , further comprising: a first level shift means that is configured to provide the second reference signal by shifting a DC level that is associated with the first reference signal. 
   
   
     16. The temperature compensated function generator circuit as in  claim 15 , further comprising:
 a third square function generator circuit having an inverting input that is configured to receive the first reference signal, and further having a non-inverting input that is configured to receive the first reference signal, wherein the third square function generator circuit is coupled to the output of the error amplifier circuit such that the error amplifier circuit is arranged to adjust the tail current of the third square function generator circuit; and 
 a second level shift means that is configured to provide the third reference signal by shifting another DC level that is associated with an output of the third square function generator circuit. 
 
   
   
     17. The temperature compensated function generator circuit as in  claim 14 , wherein the first and second square function generator circuits each comprise:
 a first transistor having a gate that corresponds to the non-inverting input of the square function generator circuit; 
 a second transistor having a source that is coupled to a source of the first transistor, and a gate that corresponds to the inverting output of the square function generator circuit; 
 a third transistor having a drain that is coupled to the source of the first transistor, and a gate that is coupled to the output of the error amplifier circuit; 
 a fourth transistor having a gate that is coupled to a gate of the third transistor, a source that is coupled to a source of the third transistor, and a drain that is coupled to a drain of the first transistor and a drain of the second transistor, wherein the drain of the fourth transistor corresponds to the output of the square function generator circuit; 
 a first means for current limiting that is coupled between the drain of the first transistor and a first node; and 
 a second means for current limiting that is coupled between the drain of the second transistor and the first node. 
 
   
   
     18. The temperature compensated function generator circuit as in  claim 17 , wherein each of the plurality of square function generator circuits further comprises:
 a first means for buffering having an input that is coupled to the drain of the first transistor, and an output that is coupled to the drain of the fourth transistor; and 
 a second means for buffering having an input that is coupled to the drain of the second transistor, and an output that is coupled to the drain of the fourth transistor. 
 
   
   
     19. A temperature compensated function generator circuit, comprising:
 a first square function generator means; 
 a second square function generator means that is matched to the first square function generator means; 
 a means for generating an error signal with the second square function generator means, wherein the error signal includes a temperature based error that is associated with the second square function generator means; and 
 a means for compensation that is configured to adjust a control signal in response to the error signal such that an operating current associated with the first and second square function generator is adjusted to compensate for the temperature based error. 
 
   
   
     20. A temperature compensated function generator circuit as in  claim 19 , further comprising: a third square function generator means that is matched to the first and second square function generator means, wherein the third square function generator means is configured to provide a reference signal to the means for generating an error signal.